Tie line circuit arrangement



Dec. 5, 1950 K. L. BURGENER TIE LINE CIRCUIT ARRANGEMENT Filed Feb. 8, 1946 INVENTOR. KARL L. BURGENER ATTORNEY Patented Dec. 5, 1950 NITED STATES TENT OFFICE TIE LINE CIRCUIT ARRANGEMENT Application February 8, 1946, Serial No. 646,463

14 Claims.

The present invention relates to telephone exchange systems in general, and more particularly vto improved circuit arrangements for interconnecting two or more exchanges.

An object of the invention is to provide new and novel trunk circuit arrangements for joining a switchboard located in one branch exchange with a switchboard located in another branch exchange in order that connections may be established between telephone lines of difierent characters terminating at the respective branch exchange switchboards, and also connections between telephone lines terminating at the switchboard in one of the branch exchanges and telephone lines terminating in a main exchange, these latter connections being established in tandem through the switchboard located in the other branch exchange.

A feature of the invention is the provision of a novel tie line circuit for use between exchanges wherein improved means are employed to assure the proper transmission battery and supervisory arrangements to the connecting exchanges, dependent upon the character or class of connection being established.

Another feature of the invention relates to a tie line circuit wherein the same improved supervisory means as those previously mentioned are utilized to care for the supervisory conditions imposed when one end of the tie line circuit terminates in a local battery exchange or a local battery telephone.

A further feature of the invention resides in the circuit arrangement wherein a wet bridge normally connected across the talking conductors of the tie line circuit either remains so connected or is disconnected therefrom responsive to the tie line circuit being seized at one of the connecting exchanges for the extension of a particular class of call to the other connecting exchange, and in the cases where the wet bridge is so disconnected a dry bridge is partially connected in place of the wet bridge, the partial connection of the dry bridge being completed when the tie line circuit is seized at the second exchange.

A still further feature of the invention is that a wet bridge connected across the talking conductors of the tie line circuit is controllable from one end of the tie line circuit, and a dry bridge when connected across the talk ng conductors of the tie line circuit is controllable from either end of the tie line circuit.

There are other objects and features of the invention having to do for the most part with the circuit details necessary to carry out the fore-.

going.

The various objects and features of the invention will be understood best from a perusal of the following detail description in connection with the accompanying drawing, comprising Figs. 1 to 5 inclusive, which illustrates one embodiment of the invention. This drawing shows by means of the usual circuit diagrams a sufficient amount of apparatus to enable the invention to be described and understood.

Referring now to the drawing:

Fig. 1 shows a jack ending common battery circuit utilizing the present invention, the T and R terminals of which are connected to a conventional common battery manual switchboard to serve as a two-way trunk circuit for the switchboard. t should be understood, however, that the T and R terminals of Fig. 1 may be connected to a common battery telephone instrument instead of to a manual switchboard.

Fig. 2 shows a jack ending magneto, or local battery, circuit utilizing the present invention, the T and R, terminals of which are connected to a local battery telephone instrument to serve as a two-way subscribers line circuit. It should be understood in the case of Fig. 2 that the T and R terminals may be alternatively connected to a local battery manual switchboard to serve as a two-way trunk circuit.

Fig. 3 shows a conventional jack ending two way common battery ring down circuit, the T and R terminals of which are connected to a common battery main exchange of either the manual or automatic type to serve as a two-way trunk circuit for the main exchange.

Fig. 4 shows a simple jack ending circuit, the T and R terminals of which are connected to a conventional common battery telephone instrument to serve as a one-way line circuit for incoming calls only to the telephone instrument.

Fig. 5 shows a skeletonized cord circuit which provides means for completing inter-connections between the jack ending circuits of Figs. 1, 2, 3

" and' i. Keys, relays, signals, etc, not essentially necessary for an understanding of the functioning of the cord circuit with respect to the jack ending circuits of Figs. 1, 2, 3 and 4 have been omitted from Fig. 5 for the sake of clarity. It should be understood, however, that the cord circuit may be fitted with facilities to accomplish any combinations of well-known functions asscciated with a manual telephone switchboard, as, for example, the cord circuit shown in Fig. 2

3 of Patent No. Re. 18,076, C. E. Lomax, dated May 19, 1931.

Assuming that the jacks and call lamp signals of Figs. 1, 2 and 3 and the jacks of Fig. 4 are mounted in the face panels of a manual switchboard equipped with cord circuits of the type shown in Fig. 5 and located in a branch exchange which is intermediate to the distant branch exchange and the main exchange, a description of the various interconnections which can be made between the four types of jack ending circuits under the conditions outlined in this paragraph will now be given.

First, a call originated in the distant branch exchange for connection with a telephone line located in the main exchange will be traced. A substation 35 connected to the, distant branc exchange signals the operator thereat in a wellknown manner, and the operator extends the connection to Fig. l trunk circuit leading to the intermediate branch exchange switchboard, thus closing a loop across the T and R terminals of Fig. l trunk circuit. Relay Gil responds to the loop closure and, at armature ill and working contact, completes the circuit of the trunk call lamp-l5 at the intermediate branch exchange switchboard from ground, armature 1i and working contact, armature H and resting contact, trunk call lamp it; to battery.

The operator at the intermediate branch exchange responding to the trunk call inserts plug P (Fig. 5) into jack J of the calling trunk circuit, thereby causing relay ill to operate over an obvious circuit and retire trunk call lamp l5 at armature Ii. The operation of relay IE1 also closes the ring conductor of the trunk at armature l2. The insertion of plug P into jack J also completes a circuit through relays 2B and 80 from ground, winding of relay 2G, sleeve of jack J, sleeve of plug P, winding of relay 80 to battery, causing relays 2 6 and 88 to operate. Relay Zii disconnects battery and ground from impedance coil 2:33, and relay 8&3 prepares part of a circuit for supervisory lamp signal 85. Although relay i6 is bridged across the talking conductors of the cord circuit, it does not operate at this time because of the operation of relay 20.

The operator at the intermediate branch exchange manipulates a talk key (not shown) in the cord circuit and learns that a connection is desired to the main exchange. She then inserts plug P into jack J (Fig. 3) of an idle trunk circuit leading to the main exchange, thus extending a loop controlled by armature 42 across the T and R conductors to the main exchange. Aline relay (not shown) connected to the T and R conductors of Fig. 3 trunk circuit at the main exchange is thereby caused to operate and complete the circuit of the related trunk call lamp signal (not shown) at the main exchange. The main exchange trunk loop circuit may be traced as follows: ground over the T conductor (Fig. 3), spring 95 of jack J tip of plug P winding of series relay 6%, tip of plug P, tip of jack J, upper left-hand winding of repeat coil 50, upper winding of impedance coil 30, armature 21 and working Contact, armature 42, lower winding of impedance coil 3! lower left-hand winding of repeat coil 58, armature l2, ring of jack J, ring of plug P spring 91 of jack J R conductor to battery. Series relay 6!! also operates over the loop circuit just described to prevent relay 70 from operating and completing the circuit of cord supervisory lamp 65 at armature H.

The main exchange operator responds to the call by plugging an idle cord circuit (not shown) into the jack (not shown) terminating the Fig. 3 T and R conductors at the main exchange, thereby retiring the trunk call lamp signal at the main exchange. Armature 42 now controls the direct current loop from the main exchange cord circuit, and series relay 66 remains operated as long as relay 4B is held operated from the distant branch exchange. The main exchange operator now learns of the desired main exchange connection and extends the call to the wanted main exchange telephone line in a conventional well-known manner.

Upon the completion of the conversation between the calling substation in the distant branch exchange and the called substation in the main exchange, the calling substation gives the distant branch exchange operator disconnect supervision in the usual manner. The operator thereupon breaks the loop connection to relay 45, causing relay 453 to restore and, at armature Q2, open the direct current flow through series relay '66. Series relay G9 accordingly restores and bridges relay T0 across the talking conductors through armature 6|, causing relay it}, to operate and complete the circuit of supervisory lamptE. The glowing of cord supervisory lamp 65 serves as a disconnect signal to the intermediate branch exchange operator who then takes down plugs P and P this action restoring Fig. 1 trunk circuit to normal and, at the same time, giving disconnect supervision to the main exchange. The main exchan e operator also receives disconnect supervision from the called main exchange substation in the usual manner.

At the time the distant exchange branch, operator disconnected the loop circuit to relay 411, as explained in the preceding paragraph, the restoration of relay li! also closed a circuit to the Fig. 1 trunk circuit call lamp 15 from ground, armature ll and resting contact, armature ll and working contact, call lamp [,5 to battery, causing call lamp I5 to glow. On the type of connection just described, however, the intermediate branch exchange operator ignores the glowing of call lamp 1% when, the distantv branch exchange operator causes relay 49 to restore, because the glowing of cord supervisory lamp. 65. at the same time constitutes a positive disconnect signal to the intermediate branch exchange,

operator. The purpose of having trunk ca-ll lamp.

!5 glow on a plugged up Fig; l trunk circuit will be explained later in the description of another type of connection.

Second, a call originated in the main exchange for connection with a substation located in the, distant branch exchange will now be traced. A telephone line connected to. the main exchange signals the operator thereat in the usual manner, and the operator extends the connectionto a trunk circuit leading; to the intermediate branch exchange by connecting with the 'l and; R con-v ductors of Fig. 3. Ringing current from the main exchange across the T' and R conductors of Fig. 3 causes relay 9 to operate and. look through its second Winding togmundsupplied through spring 98 of jack- J? and armature 9!. The locking of relay 96 completes an obvious circuit to the related trunk cal-1 lam-p signal: at the intermediate branch exchange. I

The. operator at the, intermediate branch ex-w change responding to the trunk call inserts plug P (Fig. 5) into jack J of the calling trunk circuit, thereby opening the lock circuit of relay 90 at spring 98 and removing the ring-up winding of relay 9!] from the T and R. conductors at springs 96 and 91. The intermediate branch exchange operator then operates a talk key (not shown) in the cord circuit and learns that a connection is desired to the distant branch exchange. She next inserts plug P into jack J of an idle trunk circuit leading to the distant branch exchange, causing relays Ill, 21} and 80 to operate, as previously explained. These three relays perform no important functions at this time, The intermediate branch exchange operator next operates the individual ringing key 25 associated with the trunk circuit to signal the distant branch exchange.

- The operator at the distant branch exchange responding to the trunk call closes a loop across the T and R conductors of Fig. 1 trunk circuit. Relay 4E3 responds to the loop closure and, at armature 42, completes a loop circuit across the talking conductors to the left of repeat coil 50 and extending through Fig. 5 cord circuit all the way back to the calling main exchange. Battery and ground from the main exchange cord circuit over the last mentioned loop circuit causes series relay 60 in Fig. 5 cord circuit to operate and remove relay Ill from in bridge of the talking conductors at armature 5!. The distant branch exchange operator now learns of the desired branch exchange connection and extends the call to the wanted branch exchange telephone line in a conventional well-known manner.

Upon the completion of the conversation between the calling substation in the main exchange and the called substation in the distant branch exchange, the calling substation gives the main ofiice operator disconnect supervision in the usual manner. Similarly, the called substation gives the distant branch exchange operator disconnect supervision, and the distant branch exchange operator thereupon disconnects from Fig. 1 trunk circuit and thereby causes relay 40 to restore. The restoration of relay Bu opens the loop circuit from the main exchange through series relay 6!] at armature 42, causing series relay 5!? to restore and re-connect relay 5!! in bridge of the talking conductors at armature BI. Relay l now operates over the loop circuit from the main exchange, and Fig. cord circuit supervisory lamp 65 glows from ground, winding of relay 2! sleeve of jack J, sleeve of plug P, armature 8|, armature II, supervisory lamp 65 to battery. The intermediate branch exchange operator takes down plugs P and P and the resultant breaking of the battery and ground loop from the main eX- change cord circuit gives the main exchange operator disconnect supervision from the intermediate branch exchange. The main exchange operator now has double disconnect supervision.

As in the case of the first described connection between the distant branch exchange and the main exchange, trunk call lamp I5 also glows when the distant branch exchange operator opens the loop circuit to relay 40 on this connection but in this instance also the intermediate branch exchange operator accepts the glowing of cord supervisory lamp 65 as a positive disconnect signal.

Third, a call originated in the distant branch exchange for connection with the magneto tele phone substation I35 (Fig. 2) will now be described. Substation 35 connected to the distant.

branch exchange signals the operator thereat in a well-known manner, and the operator extends the connection to Fig. 1 trunk circuit leading to the intermediate branch exchange switchboard, thus closing a loop across the T and R terminals of Fig. 1 trunk circuit. Relay responds to the loop closure and, at armature 4| and workin contact, completes the circuit to trunk call lamp I5 from ground, armature II and working contact, armature II and resting contact, trunk call lamp I5 to battery.

The intermediate branch exchange operator responding to the call inserts plug P into jack. J of the calling trunk circuit, thereby causing relay ID to operate over anobvious circuit. The operation of relay I 0 retires trunk call lamp I5 at arma-' ture I I and closes the ring conductor of the trunk circuit at armature I2. The insertion of plug P into jack J also completes a circuit through relays 20 and 85 from ground, winding of relay 20;

sleeve of jack J, sleeve of plug P, windin of relay 86 to battery, causing relays 25 and 80 to operate. Relay 20 disconnects battery and ground from impedance coil 39, and relay 8! prepares part of a circuit for supervisory lamp 65.

The intermediate branch exchange operatormanipulates a talk key (not shown) in the cordcircuit and learns that a connection is desired to the local battery substation I35, the line circuit of which terminates in jack J at the intermediate branch exchange switchboard. She then inserts plug P into jack J and operates the individual ringing key I25 of Fig. 2 line circuit to signal telephone I35, The insertion of plug P into jack J causes relay I II] to operate over an obvious circuit and close the line circuit ring conductor to Fig. 5 cord circuit at armature I I2. The closure of the ring conductor at armature II2 causes series relay in the cord circuit to operate from ground, armature I2I and resting contact, upper winding of impedance coil I30, upper left-hand winding of repeat coil I55, tip of jack J tip of plug P winding of series relay 6U, tip of plug P, tip of jack J, upper left-hand winding of repeat coil 50, upper winding of impedance coil 38, armature 2I and working contact, armature 42, lower winding of impedance coil 35, lower lefthand winding of repeat coil 50, armature I2, ring of jack J, ring of plug P, ring of plug P ring of jack J armature II2, lower left-hand winding of repeat coil I511, lower winding of impedance coil I30, armature I22 to battery. The operation of series relay 60 opens the circuit to relay I0, thus retaining cord supervisory lamp dark.

Substation I35 responds to the signalling from ringing key I25, and the voice transmission circult is now complete between substations 35 and I35. Upon the termination of the conversation between substations 35 and i355, disconnect supervision is given to the distant branch exchange operator by substation 35 in the usual manner. The operator thereupon breaks the loop connection to relay 40, causing relay 45 to restore and, at armature 42, open the direct current flow through series relay 60. Series relay G5 accordingly restores and bridges relay I9 across the talking conductors through armature 6i, causing relay I5 to operate and complete the circuit of supervisory lamp 85. The glowing of cord supervisory lamp 65 serves as a disconnect signal to the intermediate branch exchange operator who then takes down plugs P and P this action restoring Fig. 1 trunk circuit and Fig. 2 line circuit to normal.

j 'As inthe cases of the previously described con=z assassa nections between the distant branch exchange and-'- the main exchange, trunk call lamp i also glows when the distant branch exchange operator opens the loopcircuit to relay it on this connection, but in this last instance alsov the intermediate brarrch exchange operator accepts the. glowing of cord supervisory 55 as a positive disconnect signal.

Fourth, a call originated by local battery substation I35 for connection with substation 35 in. the distant branch exchange will now be described. Substation I3'5 operates the handgenerator associated with the substation in-thezusual manner, causing alternating current relay Hill to operate and close an obvious circuit to. re lay Hi0. Relay I48 in operating locks to ground? through armatures H3 and I43: and closes the circuit to line lamp call signal M 5 from ground; armature I'4I, armature IIil', line lamp lilfii to battery.

The intermediate branch exchange operator responding to the glowing of'line lamp signal I inserts plug P into jack J of the calling line circuit, thereby causing relays 85, i i6 and IZii: to operate over obvious circuits. At armature II'I, relay I-IB opens the circuit of'line lamp I I5: at armature H2, closes the ring conductor of the line circuit; and, at armaturel3, opensthe lock circuit of relay M8 and thus causes relay MS" to restore. Relay I29 removes battery and ground from the windings of impedance coil 53 The intermediate branch exchange operator manipulates a talk key- (not shown) in the cord circuit and learns that substation E35 desires a connection with substation 35 in the distant branch exchange. She then-insertsplug P into jack J of an idle Fig. 1 trunk circuit leading to the distant branch exchange, causing relay I i! to operate over an obvious circuit and complete the ring conductor of Fig. 1 trunk circuit at armature I2. A loop circuit through series relay fifiis thus closed from ground, armature 21' and resting contact, upper winding of impedance coilv 30, upper left-hand winding of repeat coil as, tip of jack J, tip of plug P winding. of series relay 6B, tip of plug P, tipof jack J upperlef-t hand winding ofrepeat coil- H55, upper winding of impedance coil 638, armature 12 i and working con-- tact, amature M2, lower winding of impedance coil I30, lower left-hand winding of repeat coil I50, armature i i-2, ring of jack J ring of plug P, ring of plug P ring ofjalck J, armature l 2, lower left-hand winding of repeat coil 51!, lower winding of impedance coil 33, armature 22 to battery. Series relay Eli opens the circuit of relay it, thus retaining supervisory lamp 55 dark. The inter-- mediate branch exchange operator next operates individual ringing key 25 associated with Fig. 1 trunk circuit to signal the distant branch exchange.

The operator at the distant branch exchange responding to the call closes a loop across the T and R conductors of Fig. 1 trunk circuit. Relay 40 responds but performs no important functions at this time. l he operator now learns that a connection is desired with substation 35 and ex tends the call to-substation 35 in a conventionalwell-known manner.

Upon the termination of the conversation be tween substations I35 and. 35, substation its gives disconnect. supervision tothe intermediate branch exchange switchboard by operating his hand generator momentarily. Relay M0 is thus caused to operate and open the loop through series relay 6!) at: armature I42 for an interval erat e and disconnect relay 19 which in turn opens.

thecircuit of supervisory lamp 65. Should" the; intermediate branch exchange operator fail to observe the ring-01f supervision; disconnect. supervison is obtaned in the following manner.

. Substation 35- gives the distant branch exchange operator'disconnect supervision in a well-known manner, and'the operator thereupon breaks the loop connection to relay 60, causing relay 40 torestore. Relay 40 completes the circuit to trunk call lamp from ground, armature: and rest-- ing contact, armature ii and working contact, trunk call lamp i5 to battery, causing lamp I5 to glow. The intermediatebranch exchangeoperator noting lamp I5 glowing while plugv P is; in jack J accepts this signal as a disconnect signal and, consequently, takes down plugs P and; P thus restoring Fig. 1 trunk circuit and Fig. 2 line circuit to normal.

Fifth, acall originated in the distant branch exchange for connection with common batterytelephone i l-5 (Fig. 4') will now be described. Substation 35 connected to the distant branch; exchange signals the operator thereat in a wellknown manner, and the operator extends the connection to Fig. 1 trunk circuit leading to theintermediate branch exchange switchboard, thus closinga loop across the T and R terminals.- of Fig. 1 trunk circuit. Relay 4% responds and; at: armature 4i and Working contact, completest-he circuit to trunk call lamp I 5 from ground, armature ti and working contact, armature II and; resting contact, trunk call lamp I5- to battery.

The intermediate branch exchange operator responding to the call inserts plug P into jack J- of the calling trunk circuit, thereby causing re lay ll to operate over an obvious circuit. Theoperation of relay. I9 retires trunk call lamp I5 atarmature II and closes the ring conductor-of the trunk circuit atiarmature I2. The insertion. of plug P into jack J- also completes a circuit through relays 2e and 89 from ground, winding of relay 2!], sleeve of jack J; sleeve of plug: P, winding of, relay to battery, causing relays 20" and 88- to-operate. Relay 29 disconnects battery and ground from impedance coil 3B, and relay 813 performs no important function at this time.

The intermedate branch exchange operator now manipulates a talk key- (not shown) in, the cord circuit and learns that a connection is desired to common battery substation I25, theline circuit of which terminates in jack J at. the intermediate branch exchange switchboard. The operator noting that a connection, to common battery substation M5 is wanted, removes plug P from jack J and inserts. plug P into-jack J. The reason for switching plugs inthe trunk. circuitjack J is that it is necessary to provide transmission battery from Fig. 1 trunk circuit through Fig. 5 cord circuit to. substation I45. Relay 25 does not operate over the sleeve of plug P and, consequently, battery and ground re,-- main connected to the windings of impedance coil13i'! through armatures. 2|; and 22 and associated resting. contacts. The operator then. insertsplug P intojack' J and operates. a ringing 'aesasse key (not shown) in the cord circuit to signal substation I45. Relay 80 operates over the sleeve circuit of plug P and jack J Substation I45 responds to the signalling from the cord circuit, and the voice transmission circuit is now complete between substations 35 and I45; Transmission battery is supplied to substation !45 through impedance coil 30 and the left-hand windings of repeat coil 55, cord circuit series relay 65 operating over this direct current loop. Upon the termination of the conversation between substations 35 and M5, disconnect supervision is given to the distant branch exchange operator by substation 35 in the usual manner, and to the intermediate branch exchange operator by substation Hi5. When substation I45 returns the handset to the telephone cradle, the loop circuit through series relay (it is opened and series relay 60' restores. The restoration of series relay 60 connects relay I across the talking conductors of the cord circuit, causing relay II! to operate and complete the circuit to cord supervisory lamp 55 from ground, sleeve of jack J sleeve of plug P, armature Bl, armature 'II, lamp 65 to battery. Should the distant branch exchange operator open the loop circuit to relay 40 before the intermediate branch exchange operator takes down plgs P and P, a

circuit to trunk call lamp I would be completed from ground, armature 4! and resting contact, armature II and working contact, trunk call lamp I5 to battery. The intermediate branch exchange operator, however, ignores the glowing of trunk call lamp I5 under these conditions as she accepts the glowing of cord supervisory lamp 55 as a positive disconnect signal.

Sixth, a call originated b local battery substation I35 for connection with common battery telephone I45 (Fig. 4) will now be described. Substation I35 operates the associated hand generator in the usual manner, causing alternating current relay I60 to operate and close an obvious circuit relay I40. Relay I40 locks to ground through armatures H3 and I 43 and closes the circuit to line call lamp I I5 at armature I4 I. The intermediate branch exchange operator responding to the call inserts plug P into jack J thereby causing relays 80, H0 and I to operate over obvious circuits. At armature III, relay IIB opens the circuit of line lamp I5I: at armature I I2, closes the ring conductor of the line circuit; and, at armature I I3, opens the lock circuit of relay I40. Relay I20 removes battery and ground from the windings of impedance coil I30.

The intermediate branch exchange operator manipulates a talk key (not shown) in the cord circuit and learns that a connection is desired to common battery substation I 45. The operator then removes plug P from jack J and in-- serts plug-P into jack J Relay I 20 does not operate over the sleeve of plug P and, consequently, battery and ground are connected to the windings of impedance coil I through armatures I2I and I22 and associated resting contacts. The operator next inserts plug P into jack J and operates a ringing key (not shown) in the cord circuit to signal substation I45. Relay 80 operates over the sleeve circuit of plug P and jack J Substation I45 responds to the signalling from the cord circuit, and the voice transmission circuit is complete between substations I and I45. Transmission battery is supplied to substation I through impedance coil I30 and the lefthandwindings of repeat coil I55, cord circuit 56- 1 ries relay 60' operating over this direct current loop. Upon the termination of the conversation between substations i353 and I45, series relay -60 restores and connects relay iii across the cord circuit, and the cord supervisory lamp glows fromground, sleeve of jack J sleeve of plug P, armature SI, armature ll, lamp 65 to battery. The intermediate branch exchange operator takes down plugs P and. P to restore the circuits to normal.

Seventh, a call originated by local battery substation !35 for connection with a telephone line located in the main exchange will now be described. Substation I35 operates the hand generator, causing alternating current relay I'60 to operate and close an obvious circuit to relay I40.

Relay I40 locks to ground through armatures I I3 and I 43 and completes the circuit to line call lamp H5 at armature I 4! The intermediate branch exchange operator responding to the call inserts "plug P into jack J thereby causing relays 80, III! and I20 to operate over obvious circuits.

"At armature II I, relay IIO opens the circuit of line'lamp H5: at armature II2, closes the ring conductor of the line circuit; and, at armature II 3, opens thelock circuit of relay I40. Relay I20 removes battery and ground from the windings of impedance coil I30.

The intermediate branch exchange operator then manipulates a talk key (not shown) in the cord circuit and learns that a connection is desired to the main exchange. She next inserts plug P into jack J of an idle trunk circuit leading to the main exchange, thus extending a loop controlled by armature I42 across the T and R conductors to the main exchange. A line relay (not shown) connected to the T and R conductors of Fig. 3 trunk circuit at the main exchange is thereby caused to operate and complete the circuit of the related trunk call lamp signal (not shown) at the main exchange.

The main exchange operator responds to the call by plugging an idle cord circuit (not shown) into the jack (not shown) terminating the Fig. 3 T and R conductors at the main exchange, thereby retiring the trunk call lamp signal at the main exchange. Normally closed armature I42 now controls the direct current loop from the main exchange, and series relay as remains operated as long as relay-I50 is in the normalposition. The main exchange operator now learns of the desired main exchange connection and extends the call to the wanted telephone line in a conventional well-known manner.

Upon the termination of the conversation between substation i35 and the called substation in the main exchange, substation I35 gives disconnectsupervision to the intermediate branch exchange switchboard byoperating the hand generator. Relay M0 is thus caused to operate and open the loop through series relay 60 at armature M2. Series relay 50 accordingly restores and connects relay I0 across Fig. 5 cord circuit to operate from battery and ground supplied from the main exchange. Relay l0 completes the, circuit to supervisory lamp 65 at armaturefII. The intermediate branch exchange operator takes down plugs P and P thus giving disconnect supervision to the main exchange. The main exchange operator also receives disconnect supervision from the called main exchange substation in the usual manner.

' Eighth, a call originated in the main exchange for connection with substation I35 will now be described. A telephone line circuitconnectedto the main-exchange signals the operator thereat in the usual manner, and the operator extends the connection to a trunk circuit leading to the intermediate branch exchange. Ringing current 'from the main exchange across the T andR-con- 'ductors of Fig. 3 causes relay 90 to operate and :lock through its second winding to ground supplied through spring 98 of jack J and armature 9|. circuit to trunk call .lamp '95 at the intermediate branchexchange.

The operator at the intermediate branchexchange responding to :the'trunk call inserts plug P into jack J of the calling trunkcircuit, :thereby opening the 'lock'circuitof relay 90 :at spring 98 and removing the ring-up winding of relay *90 from the Ttand R, conductors "at springs 96 and 91. The "operator then manipulates a talk key (not shown) in the *cord circuitand learns that .a :connection is =des'i'red to substation 1-3 5. She nextinserts plug P into jack J and operates the individual ringing key l2'5 of Fig. 2 line circuit to signal telephone I35. The insertionofplug-P into jack J causes relays 80, l'lfl and 120 to=oper- 1 fcuit is now complete between the calling :main

exchange substation and substation 1-35. Upon the termination of the conversation, the calling -substation'gives the main exchange operatordisconnect supervision in :the usual manner. Sub- The locking of relay 90 completes 'an 'obvious station 1 35 gives the intermediate branch ex- 1 change operator disconnect supervision :by operating the hand generator, thus causing relay 1.48 to operate and open the :loop circuit through series relay -60 at armature 142. Series relay 60 accordingly restores and connects relay 10 across :Fig. 5 cord circuit to operate -from battery and ground :supplied from the public exchange. Relay -|0 completes the "circuit to supervisory lamp 65 :at armature H. The intermediate :bra'nch exchange operator takes (down plugs P and P thus giving :the main exchange operator :disconnect supervision.

It is possible -to-complete a call irom th'e main exchange over Fig. 3 trunk circuitto the :intermediate branch-exchange for connection to common battery substation M5 (Fig.z4-) but nodetail description will be given because the present invention is not concerned with such a connection.

.-It-shou1d be understood at this time that while the foregoing description and associated drawing'disclose the invention as specifically applied to connecting exchanges of the :manual "switchboard type, the invention is not limited. to such exchanges but :may -be applied to any :groupv of connecting exchanges where tie .line circuits are employed.

Having described the invention and what .is considered 'new and desired to be protected by Letters "Patent issetfo'rth in the folrowin'g claims '1. In a trunk'ci'rcuit havin'g'apair of conductors, a winding, 'a circuit connectedin 'bridge'of said conductors through said winding, an incomplete circuit, a jack having terminals, a relay connected to one of said terminals and o erated thereover iordisabling said first circuit and for- 12 bridging'said incomplete circuit across said conductors -through said winding, a relay operated over said trunk circuit ifor completing said incomplete circuit bridged across said conductors,

said last-completed circuit thereafter controlled 'by said last relay.

2. In a trunk circuit, conductors. a double wound coil, power source connected through both windings of said coil in circuit with said .cnductors, means for disconnecting said power source from said windings, a partly prepared dry circuit, means for further preparing said partly prepared dr-y circuit, and a relay later operated 'over said trunk circuitfor completing said Thirther prepared-dry circuit through said windings.

3. In a trunk circuit having two pairs of con ductors linked together, a c'oil having two windings normally connected in bridge of one pairoi said conductors, a jack :having three or more terminals, said one *pairof conductors terminating in twoofsaid terminals, a relayconnectedto a third terminal of said terminals, said relay operated responsive to a circuit closure over said third terminal for disablingsaid normal circuit of said coil, and a second relay in bridge of the other pairof said conductors and operative thereover :for completing a second circuit in bridge 'of said first pair of conductors throughcontacts of said first operated relay and :both windings oi said-coil.

i. In a trunk circuit, two pairs of conductors inductively'coupled together, acircuit connected in bridge of one of said pairs of conductors, means for openingsaid connected circuit and partly connecting a second circuit in bridge of said one pair of conductors, and a relay in bridge of said other :pair of conductors "and operative thereover for completing and controlling said second-circuit at will.

5. In a trunk circuit, two pairs of conductors, means inductively intercoupling said pairs of conductorsya jack having more than one terminal, one pair of said coupled conductors terminating in two terminals 0f said jack, a double wound'rc'oil, a power source connected in circuit with said one pair of conductors through the windingsof said-coil, a relay connected in circuit with said other pair of conductors and operative thereover for partly completing a circuit through both windings of said coil in bridge of said'first pair of conductors, and another relay connected to a third terminal of said jack and operative thereover for disconnecting said power source from the windings 0i said coil and completing said "partly completed circuit' through said windings.

6. 'In a trunk "circuit, a 'jack 'having terminals, two pairs *of talking conductors, one pair of said conductors terminating intwo terminals of said jack at one end and at the other end inductively coupled tosaid second pair of conductors, a coil normally connected in bridge-of said'firstp air of conductors-a call signal, a relay responsive to-an incoming call received over "said second pair "of conductors 'for causing said call signal to operate and for partially establishing another 'circuit in bridge of saidfirst pair of-conductors for said coil, means responsive to a connection with said. jack when said incoming call is answered for disabling said call signal, for-disabling said normal bridge circuit of said coil, and for completing said partially-established circuit,

7. In a trunk circuit, two pairs of conductors, a-jack having terminals, one *pair of said conduct'ors terminating in twoterm'inals of said -J' ack at one end and at the other end inductively cou pled to said second pair of conductors, a winding normally connected in circuit with said one pair of conductors, a relay, said relay connected to a third terminal of said jack and operated responsive to a circuit closure over said third terminal for disabling said normal circuit 01'' said winding and completing a second circuit in bridge of said one pair of conductors through said winding, and means operated over said other pair of conductors later controlling said second circuit.

8. In a telephone system, a link having talking conductors, a trunk having talking conductors, a winding, a source of current connected in bridge of said talking conductors of said trunk through said winding, means in said trunk responsive to the connection of said link with said trunk for disconnecting said current source from said winding and partly establishing a dry control circuit through said winding to the talking conductors of said trunk and thereover to the talking conductors of said link, means for signalling over said trunk, and means in said trunk responsive to the answering of said signalling for completing said partly established control circuit to the talking conductors of said link for supervisory purposes.

9. In a telephone system, a trunk inductively divided into two sections, a coil, a power source connected in bridge of one of said sections through said coil, a call signal, means responsive to an incoming call received over said other section for causing said call signal to function, a dry circuit partly connected in bridge of said one section through said coil, a circuit having supervisory means for answering incoming calls on said trunk, means responsive to the connecting of said answering circuit with said one section of said trunk for disabling said call signal, for disconnecting said power source from said coil, and for completing the connection of said dry circuit in bridge of said one section through said coil, said connected dry circuit constituting a control bridge for said supervisory means of said answering circuit, said control bridge controllable over said other section.

10. In a telephone system, a cord circuit having two plugs, a jack ending trunk having talking conductors, a wet circuit connected in bridge of said conductors, a dry circuit partly connected in bridge of said conductors, said wet circuit remaining connected in bridge of said conductors when one of said plugs is inserted into the jack of said trunk, said wet circuit opened and said partly connected dry circuit completely connected in bridge of said conductors when said other plug is inserted into said jack.

11. In a telephone system, a trunk having a control bridge normally connected across its talking conductors, a second control bridge partly connected across said conductors, a link circuit having two connecting means, said first control bridge remainin connected across said conductors when one of said connecting means of said link circuit connects with said trunk, said first control bridge disconnected from said conductors and said second control bridge completely connected across said conductors when said other means of said link circuit connects with said trunk.

12. In a telephone system, a trunk having talking conductors, a relay, a circuit, a coil, said relay in one position connecting said circuit through said coil in bridge of said conductors, said relay in another position disconnecting said circuit from said coil and substituting a second circuit for said first circuit in said bridge, two connecting means for connecting with said trunk, one of said connecting means when connecting with said truk causing said relay to hold in one position, said other connecting means when connecting with said trunk causing said relay to switch to the other position.

13. In a telephone system, a trunk having a transmission battery feed normally connected in bridge of said trunk, a dry circuit partially connected in bridge of said trunk, a line of certain character, another line of different character, a link for interconnecting said trunk with either of said lines, said transmission battery feed extended from said trunk through said link to said line of said certain character responsive to the connection of said trunk with said line of said certain character by said link, said transmission battery feed thereafter controllable from said line of said certain character, means for disconnecting said transmission battery feed from in bridge of said trunk and completely connecting said partially connected dry circuit in bridge of said trunk, said completed dry bridge extended through said link to said other line of said different character responsive to the connection of said trunk with said other line of said difierent character by said link, said completed and extended dry bridge thereafter controllable over said trunk.

14. In a telephone system, a line having a current source in bridge of said line, a second line having a dry circuit partly in bridge of said second line, a trunk having an incomplete dry bridge and a complete wet bridge, a link for connecting said trunk with either of said lines, said link having a supervisory signal, means for completing said incomplete ldry bridge of said trunk, said completed dry bridge extended through said link to said current source in said first line responsive to said link connecting said trunk with said first line, said supervisory signal in said link thereafter controllable from said trunk over said completed and extended dry bridge, means for completing said partly complete dry circuit in said second line, said last completed dry circuit extended through said link to said wet bridge in said trunk responsive to said link connecting said trunk with said second line, said supervisory signal in said link now controllable from said second line over said extended dry circuit through said link.

KARL L. BURGENER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,399,998 Raynsford Dec. 13, 1921 2,073,003 Darrow Mar. 9, 1937 2,292,371 Ferrell Aug. 11, 1942 

